Internal combustion engines such as gasoline engines, diesel engines, and gaseous fuel-powered engines exhaust a complex mixture of air pollutants. In an effort to reduce the potential negative effects of these pollutants on the environment, exhaust emission standards for these engine systems have become more stringent. In fact, many industrialized countries impose environmental regulations that limit the amount of pollutants emitted to the atmosphere from an engine, depending on the type, size, and/or class of engine.
In an effort to reduce gaseous emissions, an emphasis has been placed on using electrical power to operate various components associated with a vehicle. Hybrid vehicles have been developed, for example, that rely on a combination of electrical energy and energy produced by a power source (e.g. an internal combustion engine or a fuel cell) to power certain electrical components such as, for example, traction motors for maneuvering the hybrid vehicle. Another example of an electrical accessory includes a hydraulic motor for use with heavy duty equipment such as, for example, an implement. Further, hybrid vehicles typically include one or more power storage devices (e.g. batteries) to receive and store excess electrical power from the power source and/or electrical power from regenerative dynamic braking of traction motors.
With the inclusion of power storage devices as alternate sources of electrical power, new electrical system architectures are being developed to make use of the power storage devices to increase the convenience, fuel economy, and safety of hybrid vehicles. For example, power storage devices may be configured to power the traction motors and/or electrical accessories for a limited period of time without requiring use of the power source. Thus, these architectures may reduce or eliminate fuel costs and emissions associated with the use of the power source during the limited period of time. Further, because start-up of a power source can take a relatively long period of time (e.g. five minutes for some heavy-duty hybrid vehicles), these architectures increase vehicle productivity by powering systems of the vehicle during the start-up period, thereby reducing equipment downtime during start-up.
One example of a system that provides power to accessories in a hybrid vehicle without requiring start-up of a main power unit is disclosed in U.S. Patent Application Publication 2007/0103002 (“the '002 publication”) by Chiao et al. Specifically, the '002 publication discloses a heavy-duty hybrid vehicle power system including a main power unit, a power source (e.g. batteries, ultracapacitor packs, and/or flywheels), an electric traction motor, an electric accessory motor, and a DC-DC converter to step high voltage DC power down to a level required by low voltage accessories. The main power unit provides more than 640 volts of power to a DC power bus and is configured to provide power to the power source, the electric traction motor (via a first inverter), and the electric accessory motor (via a second inverter). The power source stores power from the main power unit as well as power generated from dynamic electromagnetic braking regeneration. The first inverter converts DC power from the DC power bus to AC power, which drives the electric traction motor to propel the heavy-duty hybrid vehicle. Similarly, the second inverter converts DC power from the DC power bus to AC power, which drives the electric accessory motor. The electric accessory motor powers a belt drive assembly, which drives one or more vehicle accessories. When the main power unit is shut down, the power source supplies DC power to the first inverter and the second inverter, thereby providing power to the electric traction motor and the electric accessory motor.
While the system of the '002 publication may provide power to an electric traction motor and an electric accessory motor without operating a main power unit, it is inflexible. In particular, conversion of high voltage power, e.g., 640 volts of DC power supplied through a traction bus to a traction motor, to low voltage power, e.g., 24 volts of DC power supplied through a low voltage bus to accessories such as lights, may require multiple power conversion stages and devices. This may increase complexity and expense of the electrical system architecture. Power conversion in these types of existing devices generally requires a multi-staged device with an internal pulse width modulation (PWM) controller that can precisely control the level of voltage in the low voltage bus to meet requirements of the various low voltage accessories.
The disclosed electrical system architecture is directed to overcoming one or more of the problems set forth above.